1. Field of the Invention
A method of predicting the ultimate impact of a tropical cyclone (hurricane or typhoon) independent of local factors irrelevant to the storm itself, such as coastline shape, bathymetry, tidal cycle, flood control system, and exposure, robustness of the building code and workmanship; is based on new Wind Destructive Potential (WDP) and Storm Surge Destructive Potential (SDP) scales (the “Powell/Reinhold Scales”) which objectively rate the severity and potential impact of a tropical cyclone independent of the local factors.
2. Description of the Related Art
The Hurricane Katrina disaster and recent studies examining hurricanes and global climate change have generated discussion on tropical cyclone intensity and its relevance to destructive potential.
Climate scientists are trying to determine whether hurricanes are becoming more frequent or destructive (Webster et al., “Changes in tropical cyclone number, duration and intensity in a warming environment,” Science, Vol. 309, 1844-1846, 2005 and Emanuel, “Increasing destructiveness of tropical cyclones over the past 30 years”, Nature, Vol. 436, 686-688, 2004; each incorporated herein by reference), with resulting impacts on increasingly vulnerable coastal populations. People who lived in areas affected by, Hurricane Katrina are wondering how a storm weaker than Hurricane Camille at landfall, could have contributed to so much more destruction. While intensity provides a measure to compare the maximum sustained surface winds (Vms) of different storms, it is a poor measure of the destructive potential of a storm since it does not account for storm size. The Saffir-Simpson (SS) scale is currently used to communicate the disaster potential of hurricanes in the Western Hemisphere. While it serves a useful purpose for communicating risk to individuals and communities, it is a poor measure of destructive potential of a hurricane because it depends only on intensity. Kantha initiated debate on retiring the Saffir-Simpson scale; See Kantha, “Time to replace the Saffir-Simpson Hurricane Scale?” Eos, Trans. Amer. Geophys. Union, Vol. 87, 3-6 (2006), incorporated herein by reference.
Destruction can be qualified in terms of mortality and economic loss, but these measures cannot easily be associated with hurricanes of a given size and intensity because they also depend on population density and coastal vulnerability in the affected areas. Mortality is complicated by direct and indirect causes (Combs et al., “Deaths Related to Hurricane Andrew in Florida and Louisiana”, Int. J. Epidemiol., Vol. 25, 537-544, 1992 and Shultz et al. “Epidemiology of tropical cyclones: The dynamics of disaster, disease, and development”, Epidemiol. Rev., Vol. 27, 21-35, 2005; each incorporated herein by reference), while total insured or estimated economic loss additionally depends on the wealth of the affected areas. Therefore, mortality and insured losses do not necessarily scale within hurricane intensity. For example, the south Florida landfall of Hurricane Andrew (1992) contributed to insured losses of $22 billion (in 2006 dollars) with forty (40) deaths in Miami-Dade County while SS 3 scale Hurricane Katrina (2005) is associated with insured losses of over $42 billion and over 1,400 deaths in Louisiana and Mississippi.
Tropical cyclone intensity in the Atlantic Basin is currently defined by the National Weather Service ((NWS) 2006: Tropical Cyclone Definitions National Weather Service Manual 10-604) as the maximum sustained wind, “the highest one-minute average wind, VMS, (at an elevation of 10 m with an unobstructed exposure) associated with that weather system at a particular point in time,” and a 1-5 damage potential rating is assigned by the Saffir-Simpson scale (Simpson, The hurricane disaster potential scale, Weatherwise, Vol. 27, 169-186, 1974; Saffir, Low cost construction resistant to earthquakes and hurricanes ST/EJA/23, United Nations 216 pp., 1975; more information available from the world wide web at nhc.noaa.gov/aboutsshs.shtml, each incorporated herein by reference). From a practical standpoint, we interpret the VMS as a marine exposure wind. Determination of tropical cyclone intensity often depends on indirect estimates from visible satellite imagery (Dvorak: Tropical cyclone intensity analysis and forecasting from satellite imagery, Mon. Wea. Rev., Vol. 103, 420-430, 1975), pressure-wind relationships (e.g., Kraft: The hurricane's central pressure and highest wind, Mar. Wea. Log., Vol. 5, 157, 1961), or empirical reduction of flight-level reconnaissance wind measurements to produce surface level estimates (Franklin et al.: GPS dropwindsonde wind profiles in hurricanes and their operational implications, Wea. Forecasting, Vol. 18, 3244, 2003), each incorporated herein by reference. Coastal communities are warned for tropical cyclone impacts based on intensity information with uncertainties of 10%-20% [depending on the method and measurement platform (Franklin, supra; Uhlhorn and Black: Verification of remotely sensed sea surface winds in hurricanes, J. Atmos. Oceanic Technology, Vol. 20, 99-116, 2003), each incorporated herein by reference], and forecasts (24 h) with about 5 m/s mean absolute intensity errors (world wide web at nhc.noaa.gov/verification/Tndes.shtml?), or about one-half an SS category.
Alternative measures to assess hurricane destructive potential include accumulated cyclone energy (ASCE: ASCE 7-05 “Minimum design loads for buildings and other structures”; American Society of Civil Engineers, 424 pps., 2005 and Bell et al.: Climate assessment for 1999, Bull. Amer. Meter. Soc., Vol. 81, pages 1328-1378, 2000, each incorporated by reference), hurricane outer- and inner-core strengths (Weatherford and Gray: Typhoon structure as revealed by aircraft reconnaissance, part 1: Data analysis and climatology, Mon. Wea. Rev., Vol. 116, pages 1032-1043, 1988); Croxford and Barnes: Inner core strength of Atlantic tropical cyclones, Mon. Wee. Rev., Vol. 130, pages 127-139, 2002, Roof cladding fatigue index (Mahendran: Cyclone intensity categories. Wea. Forecasting, Vol. 13, pages 878-883, 1998), Turbulence kinetic energy dissipation (Businger and Businger: Viscous dissipation of turbulence kinetic energy in storms. J. Atmos. Sco., Vol. 58, pages 3793-3796, 2001), Power (Emanuel, supra), and Hurricane intensity and hazard indices, Kantha, supra). Most of these measures have limitations related to the lack of information on the spacial extent of damaging winds. For example, ACE and power are computed from the square or cube of VMS without considering storm structure.
Mahendran, supra, was the first to call attention to the need for a damage index based on quantities other than VMS. He modeled fatigue damage to metal roofing panels and found that the damage depended on the radius of maximum wind, storm translation speed, central pressure, and maximum wind gusts.
Kantha, supra, was the first post-Katrina paper to question the SS scale. He acknowledged the importance of dynamic pressure associated with the wind and proposed a continuous hurricane intensity index (HII) based on the square of the ratio of VMS to a reference wind of 33 m/s. A 6.0 HII rating would represent a maximum sustained surface wind speed of 81 m/s. Kantha also recognized the need to account for storm size and proposed a hurricane hazard index (HHI), which brought in the radius of hurricane-force winds, the storm motion, and the cube of VMS [based on Emanuel's, supra, 2005 claim that damage scales with the third power of VMS].
The HHI has the advantage of being a continuous scale, but it is not bounded. The HHI also fails to consider that the wind field of a hurricane can be asymmetric with different wind radii in each quadrant, and become exceeding large when a storm stalls. Dependence on the cube of VMS also makes the HHI overly sensitive to a single wind speed value and a very small part of the storm, which is difficult to sample and measure. Additionally, the damage process is too complex to simply state that it depends on some power of VMS. While wind loading on a structure is related to the square of the wind speed (ASCE 7-05, supral, interactions of a structure with the wind are dependent on the structure of the turbulence, the cycling between gusts and lulls and the debris loading. A given building component may have a wind resistance or a wind vulnerability curve that depends on the strength of the local building code, code enforcement and workmanship, and that varies greatly from other components. The ultimate wind resistance of the structure system depends on the interaction of the various components. Economic loss estimates can include indirect affects beyond the physical interactions between structures and wind, such as loss of use, living expenses, food spoilage, etc., resulting in loss relationships to as high as the 9th power of the VMS (Nordhaus: The economics of hurricanes in the United States, NBER Working paper w12813 (available on the world wide web online at papers.nber.org/papers/w12813, 2006)). However, attempts to match economic loss to some power of VMS (e.g., Howard et al: The decision to seed hurricanes, Science, Vol. 176, pages 1191-1202, 1972) and Nordhaus, supra, fall prey to the same limitations as the SS scale in that they ignore the fact that loss also depends on the wealth and population density of the impacted area such that a large, but relative weak storm in a well populated area (e.g., Francis, 2004: SS 2 scale, 4.4 billion dollars) can result in higher losses (based on estimates from the American Insurance Services Group) than a smaller more intense storm hitting a less populated area (e.g., Dennis, 2005, SS 3 scale, 1.1 billion dollars).
The dynamics of risk perception are also affected insofar as people who decide to leave or stay in response to a hurricane warning make decisions based on perceived vulnerability and past hurricane experience as one of several influences on this perception (e.g., Wilkinson, et al.: Citizens' response to warnings of Hurricane Camille, Social Science Research Center Rep. 35, Mississippi State University, 56 pp., 1970). Those who have experienced significant loss from disasters are more likely to have realistic risk perceptions in response to future warnings (Shultz et al., supra, Milletti and O'Brien: Warnings during disaster: Normalizing communicated risks, Social Problems, Vol. 39, pages 40-57, 1992). In the case of Hurricane Katrina (2005) on the Mississippi coast, regardless of warnings well in advance, some people did not evacuate because their location was known to not have been flooded by Hurricane Camille, an SS 5 scale storm that devastated the area in 1969. However, despite having the same SS 5 rating the day before landfall, and a lower (SS 3) rating at landfall, Katrina's landfall wind field was much larger than Camille's (See, FIG. 1a for Hurricane Camille and FIG. 1b for Hurricane Katrina). Without storm size information and the SS classification, some people may have perceived the risk of Katrina to be the same or even lower than Camille. In Katrina's aftermath, many people in coastal Mississippi have repeated the statement attributed to Mr. Tim Hoft of Biloxi on 30 Aug. 2006: “It looks like Hurricane Camille killed more people yesterday than it did in 1969” (A. Lee, Biloxi Sun Herald, 2006). Better risk perception is an important goal for any new metric of hurricane destructive potential.
Applicants suggest that a metric relevant to the physical forces that contribute to damage, based on the size of the wind field and magnitude of the winds, will provide a better tool and method for determining destructive potential.
Applicants have taken a first step toward defining scales to help distinguish between potential wind and wave/surge impacts while retaining the concise range of the SS scale. The destructive potential is suggested as an objective starting point to estimate the impact of the wind field, before the coastal vulnerability, infrastructure, and affected populations are taken into account.